FIG. 14 illustrates an example of a conventional steering apparatus for applying a steering angle to steered wheels. In this steering apparatus, a steering shaft 3 is supported on the inner-diameter side of a cylindrical shaped steering column 2 that is supported by a vehicle body 1 so as to be able to rotate freely, and a steering wheel 4 is supported by the rear-end section of the steering shaft 3. The rotation of the steering wheel 4 is transmitted to an input shaft 8 of a steering-gear unit 7 by way of a universal joint 5a, an intermediate shaft 6 and a universal joint 5b. As the input shaft 8 rotates, a pair of tie rods 9 that are located on both side of the steering-gear unit 7 are pushed or pulled, which applies a steering angle to a pair of left and right steered wheels according to the amount that the steering wheel 4 is operated.
In the construction illustrated in FIG. 14, a telescopic mechanism is assembled for adjusting the forward/backward position of the steering wheel 4 according to the size and operating posture of the operator. The telescopic mechanism comprises a steering column 2 that is constructed by combining an inner column 10 and an outer column 11 in a telescopic shape so as to be able to freely extend or contract, and a steering shaft 3 that is constructed by combining together an outer tube 12 and an inner shaft 13 by a spline joint so that torque can be transmitted, and so as to be able to freely extend and contract.
In the illustrated example, a tilt mechanism that makes it possible to adjust the up/down position of the steering wheel 4 is also assembled. Furthermore, an electric-powered power steering apparatus having an electric motor 14 as an auxiliary power source is assembled to reduce the force necessary for operating the steering wheel 4. More specifically, a housing 15 that houses a worm gear reducer of the electric-powered steering apparatus is connected and fastened to the front-end section of the inner column 10, and the housing 15 is supported by the vehicle body 1 so as to be able to pivotally displace around a horizontal shaft 16. A displacement bracket 18 that is fastened to the outer column 11 is supported by a support bracket 17 that is supported by a different location of the vehicle body 1 so as to be able to displace freely in the forward/backward direction and up/down direction. Together with constructing the steering column 2 so as to be able to freely extend and contract, by supporting the steering column 2 such that the support bracket 17 is able to break away and displace in the forward direction due to an impact load during a secondary collision, it is also possible to construct a mechanism for reducing impact that is applied to the body of an operator that hits the steering wheel 4.
In the case of a tilt mechanism and telescopic mechanism, except for the electric-powered mechanism, the operating state is switched by the operation of an adjustment lever between a state in which the position of the steering wheel 4 can be adjusted and a state in which the adjusted position of the steering wheel 4 can be maintained. For example, in the case of the conventional construction illustrated in FIG. 15, by providing a slit 19 that extends in the axial direction on the bottom surface of the front half of the outer column 11, it is possible to elastically expand or contract the inner diameter of the front section of the outer column 11. A pair of supported sections 20 that constitute the displacement bracket 18 are fastened to portions on both sides in the width direction of the slit 19 of the outer column 11, and a longitudinally elongated hole 21 that extends in the axial direction (forward/backward direction) is formed in portions of these supported sections 20 that are aligned with each other. The support bracket 17 comprises a pair of support-plate sections 22 that are parallel with each other and that hold the pair of supported sections 20 from both sides in the width direction; and vertically elongated holes 23 that extend in the up/down direction and that are partially arc shaped around the horizontal shaft 16 are formed in these support-plate sections 22. An adjustment rod 24 is inserted through the longitudinally elongated hole 21 and the vertically elongated holes 23.
An expansion/contraction mechanism that is constructed by a cam apparatus 26 or the like, the cam apparatus 26 comprising a drive-side cam 27 and a driven-side cam 28, is assembled on the adjustment rod 24, and makes it possible to increase or reduce the space between the pair of support-plate sections 22. The driven-side cam 28 engages with a vertically elongated hole 23 that is formed in one of the support-plate sections 22 so as to be able to displace only along the vertically elongated hole 23. A nut 29 is screwed onto and fastened to a portion of the tip-end section of the adjustment rod 24, that protrudes from the outside surface of the other of the pair of support-plate sections 22, and a thrust bearing 30 and pressure plate 31 are provided between the outside surface of the other support-plate section 22 and the nut 29. An engaging piece 32 that is provided on the inside surface of the pressure plate 31 engages with the vertically elongated hole 23 that is formed in the other support-plate section 22 so as to be able to displace only along the vertically elongated hole 23.
When adjusting the position of the steering wheel 4, the adjustment lever 25 rotates and drives the drive-side cam 27, which reduces the dimension in the axial direction of the cam apparatus 26, increases the space between the driven-side cam 28 and the nut 29, and releases the force of the pair of support-plate sections 22 against the pair of supported sections 20. At the same time, the inner diameter of the portion of the front section of the outer column 11 that fits with and supports the inner column 10 is elastically expanded, reducing the pressure that acts on the area of contact between the inner-circumferential surface of the outer column 11 and the outer-circumferential surface of the inner column 10. In this state, the up/down position and forward/backward position of the steering wheel 4 can be adjusted within the range that the adjustment rod 24 is able to displace inside the longitudinally elongated hole 21 and the vertically elongated holes 23.
Rotating and driving the drive-side cam 27 in the opposite direction using the adjustment lever 25 increases the dimension in the axial direction of the cam apparatus 26, which reduces the space between the inside surfaces that face each other of the driven-side cam 28 and nut 29, and the pair of supported sections 20 are firmly held by the pair of support-plate sections 22. At the same time, the inner diameter of the portion of the front section of the outer column 11 that fits with and supports the inner column 10 is elastically reduced, and the pressure that acts on the area of contact between the inner-circumferential surface of the outer column 11 and the outer-circumferential surface of the inner column 10 increases. In this state, the up/down position and the forward/backward position of the steering wheel 4 are maintained in the adjusted positions.
In order to maintain the flexibility of the portion of the front section of the outer column 11 that fits with and supports the inner column 10, normally, the slit 19 is opened up and formed in the front-end edge of the outer column 11. In this case, the rigidity of the front-end edge of the outer column 11, which is the open end side of the slit 19, becomes a minimum, and the rigidity of the outer column 11 increases toward the closed-end side of the slit 19, so the force by which the outer column 11 supports the inner column 10 changes according to the forward/backward position of the steering wheel 4. On the other hand, it is feasible for both end sections in the forward/backward direction of the slit 19 to be closed-end sections that are not open on the end edges of the outer column; however, in that case, the force required for operating the adjustment lever increases.
WO2006/011378 (A1) discloses construction in which a slit comprises a main slit section that is formed in the axial direction, and a sub slit section that is formed in the circumferential direction on at least one end section of both end sections in the forward/backward direction of the main slit, with the end section in the axial direction of the main slit being open to the middle section in the circumferential direction of sub slit section such that the shape of the slit as seen from the radial direction is a T shape or H shape. With this construction, together with being able to maintain the flexibility of the fitting and supporting portion of the outer column and keep the force required for increasing or reducing the inner diameter of that portion low, it is possible to a certain extent to stabilize the force by which the outer column supports the inner column regardless of the forward/backward position of the steering wheel. However, with this construction as well, there is still plenty of room for improvement in order to improve the operability when adjusting the position of the steering wheel, and further stabilizing the force by which the outer column supports the inner column.